Integrated circuit package and system interface

ABSTRACT

A method for enhancing the performance of an IC package and media interface. Adding a fissure to a Flip-Chip type package improves the crosstalk performance of the package for both high and low frequencies. The wall of the fissure can be implemented with a heat spreader layer and can be connected to any AC ground such as VSS or VDD package planes. The fissures can also accommodate the ingress of an optical fiber, which allows for a direct interface with the transceivers. The direct optical fiber interface permits the removal of solder balls for high speed signal traces, with their respective vias. On-chip integrated LEDs or other similar light source transceivers can drive the high speed signal media. Selective deposition of low dielectric material can also improve the frequency response of high speed signal package traces.

TECHNICAL FIELD

Embodiments are generally related to data transmission devices andsystems. Embodiments are also related to Integrated Circuit (IC)packages and system interfaces. Embodiments are additionally related tomethods for enhancing the performance and to extend the frequency rangeof IC packages and system interfaces.

BACKGROUND OF THE INVENTION

Consumer demand for increased mobility, wireless connectivity andadvanced features have paved the way for a variety of new productsincluding advanced mobile handsets, PDAs (Personal Digital Assistants),digital cameras and camcorders, portable music players and many othersuch devices. Silicon-based solutions driving these products are morehighly integrated than ever before, as advancements in processtechnology have resulting in the delivery of System-on-a-Chip (SoC)solutions that are smaller, faster and increasingly inexpensive. Thesetrends, along with a broad range of emerging end equipment, require alarge diversity of new IC package types to meet specific applications ormarkets. Increased device complexity can generate an explosion of newcreative and disruptive technology packaging solutions and in somemarkets and applications packaging technology is a key differentiatorwhen making purchasing decisions.

Small Computer System Interface (SCSI), a parallel interface standardfor attaching peripheral devices to computers has achieved a remarkable320 Mbps data rate. Many new transmission technologies such as Ethernet,Serial Attached SCSI (SAS), Serial Advanced Technology Attachment(SATA), and Fiber Channel (FC) have bit rates in excess of 5 Gbps. Atypical channel in all of the mentioned protocols contains Signal SourceIC (i.e., Integrated circuit with driver receiver or transceiver), ICpackage enclosure (e.g., Ball-Grid-Array, Flip-Chip, Quad Flat Package,etc.), Printed Circuit Board (PCB) with a connector interface totransmission media, and transmission media (e.g., copper or fiber opticcable).

The overall system throughput can be determined by the component withthe narrowest bandwidth. Historically, the weakest link was the ICtransceiver, due to the speed limitation of the silicon and galliumarsenide manufacturing technology. As the CMOS process pushes the speedenvelope toward the 10 Gbps arena, other system components are subjectto speed limiting hurdles. Package enclosures, mother boards and mediainterface connectors are becoming the performance limits for all systemsabove the 10 Gbps data transmission range.

Integrated circuits (IC's) typically constitute devices such astransistors and diodes and elements, such as resistors and capacitors,linked together by conductive connections to form one or more functionalcircuits. IC's are typically formed in a rectangular piece of siliconreferred to as a “chip” or a “die”. Silicon dice can be formed in awafer of silicon. A wafer is a sheet of silicon with a surface that issubject to a series of fabrication steps to form a pattern of identicalIC's. The IC's are generally separated from each other by a repeatingrectangular pattern of scribe lines, also called “saw” lines located inthe surface of the wafer that serve as boundaries between the dice. Asingle IC can be formed in each die. At a late stage in a fabricationprocess, the dice are typically diced (i.e., cut apart) from the waferalong the scribe lines and each die is then bonded to a substrate toform an IC package.

Presently, the most popular IC package enclosure is the Ball-Grid-Array(BGA) package. The popularity of BGA arrangements is largely due to thelarge number of pins (e.g., exceeding 1,000 counts), small foot-print,low cost, reliability, and bandwidth adequate for present data rateswell below 10 Gbps. Referring to FIG. 1, a pictorial view of a prior artBGA package 100 is illustrated, which is a popular surface mount chippackage that utilizes a grid of solder balls 160 as its connectors.High-speed data signals enter the BGA package 100 through input ports120 located on the left side of FIG. 1, by means of bondwires 110. ICtransceivers are connected by bond wires 110 to the package posts 130.From the package posts 130, the signal flows through a package trace170, a respective via 140 and then exits the package at the solder ball160. The package traces 170 continue beyond the vias 140 toward the edgeof the BGA package 100. These extended trace sections are known as“stubs”. Any signal trace shape change from the rectangular form anddirection change from the straight line, can affect on tracecharacteristic impedance and attenuation.

The bondwires 110, with their circular cross-section, insert variabilityinto the signal propagation (i.e., attenuation and reflection). The vias140 add another discontinuity to the desired transmission lineuniformity, with their self-resonance effect. And finally, the solderballs 160 represent still another non-uniform shape and self-resonance.All such discontinuities result in signal attenuation and reflectionsand destroy the signal integrity. Equally detrimental to the signalintegrity is the cross-talk, which is due to undesirable signal couplingfrom the adjacent package traces 170. BGA crosstalk is primarily causedby bondwires 110 and package signal traces 170. Bondwires 110 and signaltraces 170 lengths are comparable and cannot be further reduced tominimize the amount of crosstalk. The IC die size can cause additionalvariability of the wirebond lengths. The effects of the solder ball 160and via 140 resonances can show up both in attenuation and the crosstalkfrequency response.

Referring to FIG. 2, a prior art graphical representation of a crosstalkresponse 150 into signal trace 23 of BGA package 100 is illustrated.Signal trace 23 is the victim trace. From the aggressor traces 17 and18, the crosstalk is generally −12 dB at 6 GHz as indicated in FIG. 2.It means that one fourth of the aggressor's transmitted signal with thethird harmonic component of 6 GHz can appear in the adjacent signaltrace 23. This precludes the use of BGA package for any datatransmission systems with a data rate above 4 Gbps.

Referring to FIG. 3, another prior art graphical representation of acrosstalk performance 200 of BGA package 100 is illustrated. Here thecrosstalk is generally in the range of −6 dB, as indicated in FIG. 3,meaning that one half of the aggressor's signal can be coupled into thevictim package trace 170 as shown in FIG. 1. For a typical differentialdrive magnitude of 1 Vpk, the coupled crosstalk would be 500 mVpk. Thisis clearly unacceptable for all known data transmission standards.

Referring to FIG. 4, a pictorial view of a prior art Flip-Chip package250 is illustrated. Flip Chip (FC) is not a specific package (such asSOIC), or even a package-type (like BGA) device. The term “Flip Chip”generally refers to the method of electrically connecting a die to apackage carrier. In contrast, the interconnection between the die andcarrier in flip chip packaging is configured through a conductive “bump”that is placed directly on the die surface. The FC package 250 depictedin FIG. 4 does not possess any bond wires, such as, for example, thebond wires 110 shown in FIG. 1. The FC package 250 is instead directlyconnected to an IC chip by means of solder bumps 410. The Flip-Chippackage crosstalk is exemplified by signal traces 420. For high densityFlip-Chip packages, the length of parallel trace coincidence can beexcessive. Layout separation is sometimes difficult to achieve, and theadvantage of the FC package 250 is lost in comparison with BGA package100 described earlier. Solder bumps 410, solder balls 160 and vias 140represent additional impedance mismatches in the transmission line,which can lead to signal reflections and further negative effects on thesignal integrity.

Referring to FIG. 5, a prior art graphical representation of thecrosstalk performance of FC package 250 depicted in FIG. 4 isillustrated. FC package 250 has an improved crosstalk performance incomparison to the BGA package 100 of approximately −18 dB. The solderbumps 410 solder balls 160 and vias 160 illustrated in FIG. 4 can causelocal extremes in frequency responses. Their removal in new packageswill further improve the attenuation and crosstalk performance.

In an effort to address the foregoing difficulties, a fissure can beadded to the Flip-Chip type of package that significantly improves thecrosstalk performance of the package for both high and low frequenciesby 70 db and 32 dB respectively, up to 20 Gbps data rates. The fissurecan be connected to any AC ground such as VSS or VDD package planes. Thefissure can also accommodate the ingress of an optical fiber, which canallow the removal of the solder balls for high speed signal traces, withtheir respective vias. On-chip integrated LEDs or similar light sourcetransceivers can drive the high speed signal media. Selective depositionof low dielectric material can improve the frequency response of highspeed signal package traces.

BRIEF SUMMARY

The following summary is provided to facilitate an understanding of someof the innovative features unique to the embodiments disclosed and isnot intended to be a full description. A full appreciation of thevarious aspects of the embodiments can be gained by taking the entirespecification, claims, drawings, and abstract as a whole.

It is, therefore, one aspect of the present invention to provide forimproved data transmission systems.

It is another aspect of the present invention to provide for an improvedintegrated circuit package and system interface.

It is another aspect of the present invention to provide for a methodfor enhancing the performance and extending the frequency range ofintegrated circuit packages and system interfaces.

It is an additional aspect of the present invention to provide for animproved IC and system interface with novel coupling configurations.

The aforementioned aspects and other objectives and advantages can nowbe achieved as described herein. A method for enhancing the performanceof Integrated Circuit packages and media interface is described, whichincludes a fissure to a Flip-Chip type package in order to improve thecrosstalk performance of the package for both high and low frequencies.The wall of the fissure can be implemented utilizing a heat spreaderlayer and can be connected to any AC ground, such as VSS or VDD packageplanes.

The fissure can also accommodate the ingress of an optical fiber, whichallows a direct interface with the transceivers. The direct opticalfiber interface can permit the removal of solder balls for high speedsignal traces, with their respective vias. On-chip integrated LED orsimilar light source transceivers can drive the high speed signal media.Selective deposition of low dielectric material can improve thefrequency response of high speed signal package traces.

Based on the foregoing, it can be appreciated that designing high-speedanalog and digital circuits for the data-communication industry is anextremely difficult task. Today, the task is especially difficult asdata rates explode well beyond 1 to 40 Gbits/s. Integrated circuits,which provide the optical-to-electronic transition for these networksystems, are the most difficult components to design in a fiber-optictransceiver. These optical electronic ICs (OEICs) include the laserdriver, generating the electrical current to modulate the laser, and thetrans-impedance amplifier, which receives a very small current from aphotodiode and must amplify it with minimal noise effects. The challengeis to accurately predict the high-speed digital-signal parasitics forthese optical systems. These parasitics are evaluated in the form ofjitter, crosstalk, skew and ground bounce, which are generated by seriesinductance on the data path, substrate coupling effects at thebulk-surface level, package structure, and board-generated effects.

Digital IC designers and IC-package designers are now encounteringhigh-frequency package limitations. Crosstalk is comprised of twosources: distributed capacitive and inductive coupling between thepackage signal lines, and common-ground inductance in the package. Thedistributed capacitive and inductive coupling, generally termed crosscoupling, can be usually modeled in microwave packages as coupledtransmission lines.

It is believed that careful selection of processing methods andmaterials can result in the successful development of production stepsfor FC devices in order to speed development of the final product.Additionally, a need exists to extend the frequency range of present ICpackages from the current range of 5 Gbps to 20 Gbps and higher forSAS/SATA/FC components. Thus, in order to meet these continuing needsand overcome the problems described above, an improved IC and systeminterface with novel coupling configurations are described in detailherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the embodiments and, together with the detaileddescription, serve to explain the embodiments disclosed herein.

FIG. 1 illustrates a pictorial view of a prior art Ball Grid Array (BGA)package;

FIG. 2 illustrates a prior art graphical representation of a crosstalkresponse into a signal trace of a BGA package;

FIG. 3 illustrates another graphical representation of a crosstalkperformance of a BGA package;

FIG. 4 illustrates a pictorial view of a prior art Flip-Chip package;

FIG. 5 illustrates a prior art graphical representation of a crosstalkperformance of Flip-Chip package;

FIG. 6 illustrates a pictorial view of two signal pair traces of an ICpackage prior to modification in accordance with a preferred embodiment;

FIG. 7 illustrates a pictorial view of an improved IC package structurewhich can be implemented, in accordance with a preferred embodiment;

FIG. 8 illustrates a detailed view of fissure structure of newIntegrated Circuit package, in accordance with a preferred embodiment;

FIG. 9 illustrates a top perspective view of an improved IC package,including a transparent image of a fissure, in accordance with apreferred embodiment;

FIG. 10 illustrates a graphic depicting crosstalk improvement in animproved IC package, in accordance with an alternative embodiment;

FIG. 11 illustrates the package boundary of an improved IC package whichcan be implemented, in accordance with an alternative embodiment; and

FIG. 12 illustrates a flowchart of operations depicting logicaloperational steps for enhancing the performance and extending thefrequency range of an IC package and system interface, in accordancewith an alternative embodiment.

DETAILED DESCRIPTION

The particular values and configurations discussed in these non-limitingexamples can be varied and are cited merely to illustrate at least oneembodiment and are not intended to limit the scope thereof.

Referring to FIG. 6, a pictorial view of two signal pair traces of anintegrated circuit package 350, prior to modification in accordance witha preferred embodiment. As illustrated in FIG. 6, four high-speed traces610 form one transmit/receive pair. Adjacent four low speed signaltraces 620 are analyzed for performance reference.

Referring to FIG. 7, a pictorial view of an improved IC package 400 isillustrated, in accordance with a preferred embodiment. Four high-speedtraces 610 as shown in FIG. 6 are enclosed by a fissure 720. The fissure720 is formed by conductive material 750 which are connected to VSS orVDD AC ground. The top of the fissure 720 can be formed by a conductiveheat spreader 730 configured from a dielectric material 740 disposed inthermal contacts 760, such that one or more arrays 770 and a layer ofthermally conductive material 750 are embedded in the dielectricmaterial 740.

The improved IC package 400 can be fabricated by forming layers ofelectrically conductive, dielectric, and thermally conductive materialson a substrate. The layers 780 are arranged to enable heat energy givenoff by current-carrying communication lines to be transferred away fromthe communication lines. The dielectric material 740 inside the fissure720 is of a low dielectric constant.

Referring to FIG. 8, a detailed view of a fissure structure 450 of theimproved IC package 400 is illustrated, in accordance with a preferredembodiment. FIG. 8 depicts in greater detail, the fissure 720 opening.Its use can be broadened to quasi-interface functions for ingress of theoptic fiber interface 810 in order to directly access data transmissionmedia. Solder bumps 410 as shown in FIG. 4 can be removed and LED lightsources can be integrated on the transceiver 820. Such a configurationcan remove the need for solder balls 160 for the most sensitivehigh-speed signal traces 610. The rest of the low-speed signal traces620 with power/ground connections can also be preserved.

Referring to FIG. 9, a top perspective view of an improved IC packageincluding a transparent image of fissure 500 is illustrated, inaccordance with a preferred embodiment. In general, an improved packagewith internal trace routing and a ground plane is repeated in FIG. 9.The size and form of the fissure 720 can be adjusted to accommodatevarious interface functions. Four high-speed traces 610 generally formone transmit/receive pair located in the fissure 720. Adjacent fourlow-speed signal traces 620 can be analyzed for performance referencewith respect to the high-speed signal traces 610. Examining a number ofpotential new approaches can yield the disclosed concept of a fullenclosure of both signal traces in a waveguide-like structure.

Referring to FIG. 10, a graph 550 of crosstalk improvement in animproved IC package 400 is illustrated, in accordance with analternative embodiment. The graph 550 depicted in FIG. 10 illustratesthe improved crosstalk performance of the improved IC package 400. Asindicated in graph 550 of FIG. 10, the high frequency crosstalk isgenerally in the range of −47 dB at 10 GHz and the low frequencycrosstalk is generally in the range of −103 dB at 2 GHz. This is asignificant improvement over the BGA and FC package worst case crosstalkof −12 dB as illustrated in FIG. 2 and −35 dB as illustrated in FIG. 5,respectively. This approach of enclosing the signal pair results in acrosstalk improvement. Such a technique also extends the use of presentmaterial packages to a frequency range up to approximately 10 GHz.

Referring to FIG. 11, the package boundary 650 of an improved IC package400 is illustrated which can be implemented, in accordance with analternative embodiment. The IC package interface with the PCB and othersystem media, can be improved for ever increasing bit rates. Forfrequency ranges above 10 GHz, the fissure 720 as shown in FIG.7 can beextended to a variety of other implementations for the I/O transceiver820 as shown in FIG. 8. The fissure 720 can be configured as a structuremade of an optical fiber material without the metal walls. At the chipend 925 the on-chip integrated LED can directly drive the optical fiberinterface 810. The fissure 720 can be extended through a PCB 910 edge.This configuration can result in the removal of solder balls 160 shownin FIG. 4 for high speed signal traces 610, utilizing their respectivevias 140. The fissure 720 can be constructed as a continuous waveguide920 with metal boundaries. At the chip end 925 of the IC package 400,the I/O can drive a loop coupling 915. The loop coupling 915 generallyserves as an input 925 to the waveguide 920. Exiting the package, thewaveguide 920 can join the similar waveguide built on the PCB 910.

Referring to FIG. 12, a flowchart of operations depicting logicaloperational steps for enhancing the performance and extending thefrequency range of an IC package and system interface 700 isillustrated, in accordance with an alternative embodiment. The processdepicted in FIG. 9 can be initiated, as indicated at block 951. Afissure can be added to a Flip-Chip type package, as depicted at block952. The fissure can be then connected to any AC ground, such as VSS orVDD package planes, as illustrated at block 953. Top wall of the fissurecan be implemented with a heat spreader layer, as indicated at block954.

Thereafter, as depicted at block 955, the fissure can accommodate theingress of an optical fiber, which promotes a direct interface with thetransceivers. The solder balls can then be removed for high speed signaltraces through direct optical fiber interface, with their respectivevias, as shown at block 956. The high speed signal media can be drivenutilizing an on-chip integrated LED or similar light sourcetransceivers, as depicted at block 957. The frequency response ofresulting high speed signal package traces can be improved by selectivedeposition of low ∈_(r) dielectric material, as illustrated at block958. The process can then terminate, as indicated at block 959.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A method for enhancing the performance and extending the frequencyrange of integrated circuit packages, comprising: adding a fissure to aFlip-Chip (FC) package in order to improve a cross talk performance ofsaid FC package for high and low frequency ranges; thereafter connectingsaid fissure to an AC ground; and configuring a top wall of said fissureutilizing a heat spreader layer in order to form an improved IC packagebased on said FC package in association with said fissure and said topwall thereof.
 2. The method of claim 1, further comprising:accommodating an ingress of an optical fiber with said fissure in orderto provide for a direct interface of said optical fiber with atransceiver; driving a high speed signal trace utilizing an on-chipintegrated light emitting device; and improving a frequency response ofsaid high speed signal trace by selectively depositing a low dielectricmaterial.
 3. The method of claim 2 wherein said light emitting devicecomprises a light emitting diode (LED).
 4. The method of claim 2 whereinsaid optical fiber permits a removal of at least one solder ball fromsaid high speed signal trace.
 5. The method of claim 2 wherein said highspeed signal trace comprises said fissure.
 6. The method of claim 1wherein said fissure extends a frequency range of said FC package. 7.The method of claim 1 further comprising: forming said fissure utilizinga conductive material in order to connect said fissure to said ACground.
 8. The method of claim 1 further comprising: associating a loopcoupling with said improved IC package, wherein at least one I/Oconnected to said improved IC package drives said loop coupling.
 9. Themethod of claim 8 wherein said loop coupling comprises an input towaveguide associated with said improved IC package and wherein saidwaveguide joins another waveguide which is configured on a PCB.
 10. Amethod for enhancing the performance and extending the frequency rangeof integrated circuit packages, comprising: adding a fissure to aFlip-Chip (FC) package in order to improve a cross talk performance ofsaid FC package for high and low frequency ranges; thereafter connectingsaid fissure to an AC ground; configuring a top wall of said fissureutilizing a heat spreader layer; accommodating an ingress of an opticalfiber with said fissure in order to provide for a direct interface ofsaid optical fiber with a transceiver; driving a high speed signal traceutilizing an on-chip integrated light emitting device; and improving afrequency response of said high speed signal trace by selectivelydepositing a low dielectric material in order to form an improved ICpackage based on said FC package in association with said fissure andsaid top wall thereof.
 11. The method of claim 10 further comprising:associating a loop coupling with said improved IC package, wherein atleast one I/O connected to said improved IC package drives said loopcoupling.
 12. The method of claim 11 wherein said loop couplingcomprises an input to waveguide associated with said improved IC packageand wherein said waveguide joins another waveguide which is configuredon a PCB.